An Ethiopian government air strike on the capital of the northern Tigray region on Friday forced a U.N. flight carrying aid workers to abort a landing there, the United Nations said.

Humanitarian sources and the Tigray People's Liberation Front (TPLF), which controls the area, said a university in Mekelle was hit by the strike.

Government spokesperson Legesse Tulu said a former military base occupied by TPLF fighters was targeted, and he denied the university was hit.

Reuters was not able to independently confirm either account. Tigrai TV, controlled by the TPLF-led regional administration that is not recognised by Addis Ababa, reported that 11 civilians were wounded in the air strike. It was the fourth day this week that Mekelle had been attacked.

The U.N. suspended all flights to Mekelle after Friday's incident. U.N. global aid chief Martin Griffiths said the U.N. had not received any prior warning of the attacks on Mekelle and had received the necessary clearances for the flight.

The incident raises serious concerns for the safety of aid workers trying to help civilians in need, Griffiths said in a statement, adding that all parties to the conflict should respect international humanitarian law including protecting humanitarian staff and assets from harm.

The 11 passengers on board Friday's flight were aid workers travelling to a region where some 7 million people, including 5 million in Tigray, need humanitarian help, another U.N. official told reporters in New York.

TPLF spokesperson Getachew Reda accused the government of putting the U.N. plane in harm's way. "Our air defence units knew the UN plane was scheduled to land (and) it was due in large measure to their restraint it was not caught in a crossfire," he said in a tweet.

Legesse, the government spokesperson, rejected the TPLF accusation. "I can assure you that there is no deliberate or intended act that put the efforts of UN humanitarian staff and their plan of delivering aid to the disadvantage (sic) group," Legesse said in a text message to Reuters.

Ethiopian army spokesperson Colonel Getnet Adene did not immediately respond to requests for comment.

PEOPLE FLEEING IN AMHARA

The two sides have been fighting for almost a year in a conflict that has killed thousands of people and displaced more than two million amid a power struggle between the TPLF and the Prime Minister Abiy Ahmed's central government.

The TPLF dominated Ethiopia's ruling party for decades before Abiy, who is not a Tigrayan, took office in 2018.

The government has stepped up air strikes on the Tigray capital as fighting has escalated in Amhara, a neighbouring region where the TPLF has seized territory that the government and allied armed Amhara armed groups are trying to recover.

Residents in Dessie, a city in Amhara, told Reuters people were fleeing, a day after a TPLF spokesperson said its forces were within artillery range of the town.

"The whole city is panicking," a resident said, adding that people who could were leaving. He said he could hear the sound of heavy gunfire on Thursday night and into the morning, and that the bus fare to the capital Addis Ababa, about 385 km (240 miles) to the south, had increased more than six-fold.

There are now more than 500,000 displaced people in the Amhara region and that number is growing rapidly due to the latest fighting, the National Disaster Risk Management Commission told Reuters.

Seid Assefa, a local official working at a coordination centre for displaced people in Dessie, said 250 people had fled there this week from fighting in the Girana area to the north.

"We now have a total of 900 (displaced people) here and we finished our food stocks three days ago."

Leul Mesfin, medical director of Dessie Hospital, told Reuters that two girls and an adult had died this week at his facility of wounds from artillery fire in the town of Wuchale, which both the government and the TPLF have described as the scene of heavy fighting over the past week.